Why Are JSON Body Expressions Not Evaluating in My n8n HTTP Request Node?

Below is an explanation of why your HTTP Request node might be sending literal expressions instead of their evaluated values and some steps you can try:

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Issue Explanation

When you enter your JSON body in the HTTP Request node using the “Using JSON” option, the node expects the input to be entirely valid JSON. In this mode, if you include parts like "text": "{{ 1 + 1 }}" (with the expression wrapped in quotes), the node treats it as a literal string rather than an expression to be evaluated.

Even when you try using variations of the syntax (or even node references like {{ $('SomeNode').item.json.someField }}), the HTTP Request node may not evaluate them because it doesn’t parse sub-parts of a JSON string as dynamic expressions. (It’s the same as if you had pasted a literal string; the conversion into actual JSON happens before any dynamic evaluation.)

This is different from the Function node where the entire parameter is interpreted as JavaScript and expressions work as expected.

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Recommended Solutions

1. Use “Using Fields Below” instead of “Using JSON”:

   When you switch to the “Using Fields Below” mode for the body, each parameter’s value can be toggled into expression mode. That way, you can directly insert an expression (without enclosing it in quotes) and let n8n evaluate it. For example, set the text field’s value to:

   JSCopied
   {{ 1 + 1 }}

   Do the same for any node references, ensuring that you aren’t wrapping your expression in additional literal quotes.

2. Wrap the Entire JSON in an Expression:

   If you need to use the “Using JSON” option for some reason (for example, because you want to send both static and dynamic values in one JSON string), you must wrap the entire JSON block in double curly brackets so that the node evaluates it as one JavaScript expression. For instance:

   JSCopied
   {{
     {
       "text": 1 + 1,
       "model_id": "eleven_monolingual_v1",
       "voice_settings": {
         "stability": 0.5,
         "similarity_boost": 0.5
       }
     }
   }}

   Notice that in this approach you remove the quotes around the expression, allowing JavaScript to compute the result.

3. Use an Upstream Node to Prepare Payload:

   As a workaround, you can prepare your dynamic JSON (e.g., in a Function node) and then pass its output to the HTTP Request node. That way, the JSON is already computed when it reaches the HTTP Request node and no further evaluation is necessary.

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Additional Considerations

• Node References: If you’re using node references (e.g., {{ $('SomeNode').item.json.someField }}) ensure that the referenced node has executed before your HTTP Request node. The HTTP Request node may otherwise treat the expression as a literal string.
• Expression Syntax: Double-check that you’re not adding extra quotes that might cause the expression to look like a plain string.

By following one of the above approaches, your HTTP Request node should substitute expressions with their evaluated values in the JSON payload rather than sending them as literal text.

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Hope this helps resolve your issue! If you continue to face this problem, consider testing with a minimal workflow to isolate whether it’s a configuration-specific issue or a broader limitation, and then double-check your node execution order.